Extrapolating branch enclosure measurements to estimates of regional scale biogenic VOC fluxes in the northwestern Mediterranean basin

Abstract

Simple summation and averaging methods were used to extrapolate 870 branch-scale measurements of volatile organic compound (VOC) emissions from 40 native Mediterranean plant species to give estimates of habitat-scale emission factors (EH) for dunes, macchia, garrigue, forest, and riverside habitats in the northwest Mediterranean area. The summation method derived biomass-weighted VOC EH using local vegetation cover data and component species emission factors and leaf area indices (LAIs). The averaging method generated mean and median EH and LAI from component species. Summer biomass-weighted EH(ng m-2 s-1) for monoterpenes and isoprene, respectively, were 1700, 125 (forest, Italy); 460, 8 (macchia, Italy); 280, 40 (dunes, Italy); 160, 1600 (forest, southern France); 34, 550 (garrigue, southern France); 0, 12000 (riverside, Spain); 90, 240 (garrigue, Spain). Autumn biomass-weighted EH(ng m-2 s-1) for monoterpenes and isoprene, respectively were 700, 31 (dunes, Italy); 2030, 1620 (forest, southern France); 64, 110 (garrigue, Spain). In general, mean and median EH underestimated biomass-weighted monoterpene EH and overestimated isoprene EH. Habitat isoprene flux estimates followed an annual cycle with a peak in summer. An autumn peak for habitat monoterpene flux estimates may be due to drought relief following autumn rains. When extrapolated to the total area of land covered by natural habitats in the northwest Mediterranean area (71,300 km2), total monoterpene and isoprene fluxes were estimated to be 0.07 and 0.1 Tg yr-1, respectively. Within the limits of uncertainty, the VOC flux estimates presented here for the Mediterranean region agree with previously published work. However, there are indications that previous published studies may underestimate monoterpene fluxes from this area. Copyright 2000 by the American Geophysical Union.